1. Field of the Invention
The present invention relates to methods and apparatus for the site-selective enhancement of a catheter which, when installed in the body of a patient, is subjected to potentially damaging stresses due to body movement. In particular, the present invention relates to a method and apparatus for enhancing the durability of such portions of a soft, medical-grade silicone rubber catheter as become implanted on a long-term basis in an area of the body subjected to repeated intermittent compressive or abrasive forces. One example of such an area is the so-called "pinch-off region" located between the clavicle and first rib, a region traversed by a central venous access catheter installed by way of the percutaneous subclavian route.
2. Background Art
Patients undergoing long-term intravenous therapy have benefited from use of indwelling central venous access catheters. The distal tip of such a catheter is entered into the cardiovascular system at a peripheral puncture site and then threaded therefrom through the cardiovascular system along a convoluted pathway to a region of high volume blood flow and turbulence near the heart, such as in the superior vena cava. Thusly positioned, the central venous access catheter remains resident for a period of time ranging from a few weeks to more than two years. During that entire residency, the catheter is agitated within the cardiovascular system seventy to eighty times per minute by the pulsating fluid flow therein produced by the action of the heart. This can rapidly produce erosion of the blood vessels where ever contact is effected by the catheter. Maximum dangers arise at bends in the cardiovascular system and at the distal tip of the catheter. In order to overcome this problem and permit the long-term implantation of central venous access catheters, such catheters are made of a soft biocompatible material, such as a medical-grade silicone rubber. It has been found that this material avoids irritating or eroding the passage ways of the cardiovascular system over long implantation periods. Once thusly implanted, such catheters have generally proven effective for the purpose of infusing chemotherapeutic drugs and antibiotics, conducting intervenous feeding, providing access for withdrawing blood samples, as well as affording access to the central venous system for any other purposes.
Nonetheless, since the introduction of indwelling central venous access catheters, a relatively constant but low level of use-related complications have been recorded relative thereto.
One group of such use-related complications is associated with indwelling central venous access catheters that are installed along pathways that traverse regions in the body subjected on a regular basis to repeated intermittent compressive or abrasive forces. In general, such stresses impose problems of long-term local wear on an implanted catheter made of a soft biocompatible material, such as silicone rubber. In such catheters repeated intermittent compressive or abrasive forces can result initially in a breech of the integrity of the lumen of the catheter at the region of wear. This in turn leads to leakage of the infusate at that point and the destruction of tissue local thereto.
Once a central venous access catheter is weakened at such a region of wear, it may even be impossible to extract the catheter in an intact condition, as such catheters are removed by pulling them out of the cardiovascular system by drawing on the proximal end thereof. In this process, a weakened catheter is likely to snap at its point of weakening leaving the distal portion of the catheter in the body of the patient.
If the catheter is not removed, however, continued local wear of an implanted venous access catheter can lead to a total severance of the catheter at the point of wear. The distal portion of the catheter is then free to migrate through the cardiovascular system raising all the risks attendant thereto. In the meantime, if undetected, the severed catheter continues in addition to emit infusate at the point of severance, instead of at a proper location with high volume blood flow and turbulence.
The problem of indwelling central venous catheter puncture or pinch-off due to compressive and abrasive forces in the body is particularly acute during the residence in the body of catheters installed along a route currently preferred by most medical professionals. This is the percutaneous subclavian route of installation, which traverses a so-called "pinch-off region" between the clavicle and first rib. Normal movement of the patient causes these two bones to closely approach each other, compressing the tissue and any catheter located therebetween. The tissue in the "pinch-off region" has adapted to these facts of anatomy and is not injured by such movement. An indwelling catheter, however, is subjected to repeated compression and abrasion, which in a predictable number of instances results in complications which have been suggested above and have been described in detail in medical literature to be cited below.
Preliminarily, however, the reader is referred to FIG. 1, which illustrates the internal anatomical features which result in repeated intermittent catheter compression and abrasion in this particular "pinch-off region" of the body. FIG. 1 is designed to assist the reader in comprehending the source of the problem of catheter failure from the action of the body in the "pinch-off region," as well as the inadequacy of efforts to date to deal with those failures. It should be understood, however, that other regions of the body traversed by long-term implantable catheters could be subjected to similar compressive and abrasive forces, and thus produce the risks associated therewith.
In FIG. 1, the upper right torso of the skeletal system and selected cardiovascular passageways of a patient are illustrated. There, right first rib A and left first rib B can be seen to be connected at the forward ends thereof by ligaments C and D, respectively, to the sternum E. The rearward ends of first rib A and second rib B are attached to a vertebrae F of the patient. Second right rib G and second left rib H are also shown for the purpose of added perspective. Each are connected at the forward ends thereof to sternum E and at the rearward ends to a vertebrae I shown below and adjacent to vertebrae F. A portion of right second rib G has been broken away in FIG. 1 in order to illustrate the superior vena cava J free of any frontal obstruction.
Also shown among the skeletal system illustrated in FIG. 1 is the right clavicle K and left clavicle L, which are each attached at the medial ends thereof by a ligament M to the top of sternum E. At the end of right clavicle K remote from sternum E, FIG. 1 includes portion of the right humerus N and right scapula O located adjacent thereto. A vertebrae Q above and adjacent to vertebrae F is also illustrated.
FIG. 1 includes with the skeletal elements just described selected components of the cardiovascular system of the patient. There the right axillary subclavian vein R can be seen to be a blood vessel returning blood from the right arm of the patient toward the heart. Axial subclavian vein R extends in the direction of that return blood flow between right clavicle K and right first rib A, thereafter to be denominated the right subclavian vein S. The external jugular vein T and the internal jugular vein U join subclavian vein S, which turns downwardly into superior vena cava J.
Normal body movements by the patient bring right clavicle K into close proximity to right first rib A regularly but intermittently, compressing therebetween axillary subclavian vein R and the tissue in the vicinity thereof. This is the area referred to with notoriety as the "pinch-off region".
The intermittent compression of the "pinch-off region" does not have adverse consequences for axillary subclavian vein R. The name attributed to the "pinch-off region" arises from the effect of the intermittent compressive and abrasive forces imposed by that region on any catheter introduced into superior vena cava J by way of being disposed in or being disposed parallel to the exterior of axillary subclavian vein R. A catheter disposed along either routes necessarily passes through the "pinch-off region". Such a catheter V is also shown in FIG. 1.
Catheter V can been seen to have been entered into the cardiovascular system of the patient at a puncture site W in axillary subclavian vein R. Catheter V extends therefrom toward the heart of the patient through the balance of the axillary subclavian vein R, through subclavian vein S, and into superior vena cava J. There the distal tip X of catheter V is intended to reside on a long-term basis. Superior vena cava J is a region of high volume blood flow and turbulence in which it is appropriate for infusate to be introduced from distal end X of catheter V. The route of insertion described above is referred to as the percutaneous subclavian route of insertion.
A catheter, installed by way of the percutaneous subclavian route can enter the cardiovascular system other than at a puncture site such as puncture site W, which is located outside of the "pinch-off region" toward the right arm. The catheter may pass through the "pinch-off region" subcutaneously, parallel to and on the exterior of the axillary subclavian vein R, thereby to actually enter the cardiovascular system at a puncture site in the subclavian vein located medial of the "pinch-off region". Nevertheless, such a catheter does not avoid the intermittent compressive and abrasive forces arising from natural body movement in the "pinch-off region". Accordingly such a catheter is also susceptible to the problems of wearing and severance discussed above.
Despite the risks of catheter wear and catheter pinch-off associated with the subclavian route of insertion for an indwelling intravenous catheter, that route of insertion is generally preferred relative to alternate routes of insertion, or to forgoing the therapeutic opportunities presented by the use of an indwelling central venous access catheter.
Below four (4) articles of medical literature will be described which report on the adverse consequences resulting to patients with indwelling catheters that traverse the "pinch-off region" illustrated in FIG. 1. Each of the four (4) articles is specifically incorporated herein by reference.
The first of these articles of medical literature is D. Aitken, et al., "The `Pinch-Off Sign`: A Warning of Impending Problems With Permanent Subclavian Catheters", 148 AM. J. SURGERY 633-36 (1984). In this article four (4) instances of complications are reported that resulted from the passage of a central venous Hickman and Broviac catheter between the clavicle and the first rib in patients requiring long-term venous access for home parenteral nutrition, frequent blood sampling, or the delivery of medication, such as chemotherapy for cancer. In one instance, catheter transection occurred at the clavicle resulting in the distal catheter segment becoming coiled in the mediastinum. The anatomy of the "pinch-off region" is explored in this article in some detail.
The second article is T Franey, et al., "Catheter Fracture and Embolization in a Totally Implanted Venous Access Catheter", 12 J. PARENTERAL AND ENTERAL NUTRITION 528-30 (1988). Reported there is the case of a totally implanted venous access system placed for chemotherapy in the body of a 24-year-old male patient with Hodgkins disease for chemotherapy. Twelve (12) months after the implantation it was noted on a chest x-ray that the catheter had fractured and that the distal fragment had embolized to the right ventricle. In the article catheter separation and embolization is stated to be a recognized but uncommon complication with Hickman catheters, as well as with other implanted central venous catheters. With the increasing use of such venous access systems, the article forecasts that these complications will become more prevalent.
The third article of medical literature is J. Noyen, et al., "Spontaneous Fracture of the Catheter of a Totally Implantable Venous Access Port: Case Report of a Rare Complication", 5 J. CLINICAL ONCOLOGY 1295-99 (1987). There the case of the spontaneous fracture of the outlet catheter of a totally implantable venous access port (IVAP) is presented. Thirty-seven (37) weeks after implantation, the outlet catheter was broken at the entrance into the left subclavian vein. The distal part was embolized in the left pulmonary artery. The embolized remnant was retrieved in an outpatient setting, using a grasping forcipal catheter through a 7 French longsheath. Experimental study of the catheter revealed that it had been broken due to a local cause, probably the longstanding compression at the narrow space between clavicle and first rib. The article emphasizes the need accordingly to ascertain the position and intactness of the outlet catheter employed with an IVAP before using that system to infuse cytostatic agents.
Finally is the article, R. Rubenstein, et al., "Hickman Catheter Separation", 9 J. PARENTERAL AND ENTERAL NUTRITION 754-57 (1985). There, seven (7) patients with Hickman/Broviac catheters implanted by the percutaneous subclavian route are reported to have had catheter separation and embolization. One catheter implanted through the cephalic vein cutdown was also separated. The method of percutaneous subclavian catheter insertion is briefly described, and the mechanism of catheter separation is discussed. Along percutaneous insertion routes between the clavicle and first rib, the body produces compressive and shearing force which can cause the silicone catheter to break-after several months. Embolized catheter fragments must be retrieved with a percutaneous transfemoral venous snare. The described complication represents a 1% incidence. Recommendations to deal with or minimize this problem mentioned in the article include chest X-rays every 2 to 3 months to identify catheter indentation at the thoracic inlet, and early removal of catheters for patients with radiologic evidence of significant catheter compression.
In summary research has indicated that the probable cause of most reported partial separations and total separations of implanted catheters in the "pinch-off region" is due to longstanding intermittent compression and abrasion of the catheter at the narrow space between the clavicle and first rib. Movement of the shoulder draws the clavicle into close proximity against the first rib exposing a catheter therein disposed to a pincher-like pressure and to repeated compressing, grinding, and rubbing. This causes the weakening that results in partial or total catheter separation.
Partial separation of the catheter can lead to various complications, the most important of which is that a hole in the catheter wall will allow the exit of infusates at an undesired location. Some infusates are extremely toxic, and the leakage thereof has required surgery to be performed to remove pockets of resulting dead tissue around the leak site.
The partial separation of a catheter can eventually progress to the separation of the catheter into two parts due to continued compression and abrasion. This results in various other complications, such as embolization. With blood flow to propel the separated distal end of the catheter, this severed portion of the catheter almost always ends up in the pulmonary vessels leading from the right ventricle to the lungs. Surgical procedures are indicated in such an event, and these result in trauma to a patient, both mentally and physically.
As mentioned above, implantable catheters of this type must be compliant due to the disposition of the catheter in relatively soft layers of tissue, including in particular the vessels of cardiovascular system. Flexibility in the catheter prevents unnecessary irritation of tissue layers and also enables the catheter to be routed through the bends in blood vessels. The effects of the imposition of compressive and abrasive forces on the soft material structure of such catheters, however, gives rise to the complications discussed above related to catheters inserted through the percutaneous subclavian route.
Efforts to solve the problem of catheter wear and catheter pinch-off have been attempted. It has been noted that the compression of the catheter may be alleviated by having patients lie supine with the arm and shoulder slightly raised. For obvious reasons, it cannot be suggested that a patient maintain such a position indefinitely. Such a procedure would require a major deviation from currently existing standard practices and would impose significant and difficult patient handling problems on medical personnel. Hence, for long-term indwelling catheters, this is not an adequate solution.
Alternately, it has been suggested to consider utilizing catheter implantation through a jugular vein, such as internal jugular vein U illustrated in FIG. 1. While use of the internal jugular vein will avoid exposing the catheter to the "pinch-off region" between the clavicle and the first rib, the entry of a catheter into a jugular vein cannot be accomplished by a percutaneous insertion. Rather, use of the jugular vein route requires a cut-down procedure, which ultimately ruins the jugular vein for any subsequent circulatory functions. Thus, this method of avoiding the risks of the "pinch-off region" requires a patient to accede to the permanent loss of a healthy jugular vein.
Alternately, it has been proposed to interweave metallic substances or other stress resistant materials in the wall of the catheter to counteract the stress imposed thereon by the body of the patient. Unfortunately, if the catheter is noncompliant or is relatively stiff, it cannot undergo easy flexing. Then the catheter is likely to irritate or damage the relatively soft layers of tissue which surround it. Again, this is an inadequate response for long-term indwelling catheters.
It has also been proposed to increase the thickness of the catheter wall in the region of anticipated wear or to mold a layer of a pliable material over the entire length of a catheter. Any measure which substantially increases the outer diameter of the catheter, however, will require enlargement of the instruments by which that catheter is inserted into the cardiovascular system. Whether the enlarged diameter is local to the region of anticipated wear or effected over the entire length of the catheter, enlarged instruments for insertion will invariably increase the trauma and seriousness of the procedures by which the catheter is inserted.
In addition, thickening the catheter, particularly over the entire length thereof, would increase the torsional rigidity of the catheter. For reasons previously set forth, such a procedure would result in a noncompliant and relatively stiff catheter which could irritate body tissues and erode areas of vital organs of the body, such as the blood vessels, where the catheter comes in contact with such organs.